Swept vane louver system



Feb. 20, 1968 J. R. ERWIN SWEPT VANE LOUVER SYSTEM 2 Sheets-Sheet 1Filed Aug. 12, 1965 INVENTOR. Jd /A ,6 fem/V Feb. 20, 1968 J. R. ERWIN3,369,773

SWEPT VANE LOUVER SYSTEM Filed Aug. 12, 1965 2 Sheets-Sheet 2 INVENTOR.JO/M/ E f/W/V 5 gw rmkw United States Patent 3,369,773 SWEPT VANE LOUVERSYSTEM John R. Erwin, Cincinnati, Ohio, assignor to General ElectricCompany, a corporation of New York Filed Aug. 12, 1965. Ser. No. 479,2537 Claims. (Cl. 244-12) ABSTRACT OF THE DISCLOSURE The invention isdirected to a louver system for vectoring the flow through aircraft liftfans. It uses swept louvers as opposed to straight and this permits aconstant flow area over a large vectoring operating range and isintended to replace vectoring cascades of vanes that are rotated belowlift fans.

The vane louver system to be described herein is applicable to eitherinlets or outlets of openings through which fluid passes but will bedescribed primarily in connection with a fluid outlet as a matter ofconvenience in illustration.

In VTOL or STOL aircraft it is desirable to vector the exhaust fromengines such as direct lift or others or from lift fans in the aircraft.The vane louver system herein is primarily directed to a more efficientmeans of vectoring the fluid discharge through an angle from thevertical to a relatively large angle for forward propulsion when appliedto aircraft of the above type. In other words, the vane louver systemherein is an effective vectoring arrangement regardless of the source ofthe fluid. For convenience, it is best described in connection with thelift fan type as shown in U.S. Patent 3,176,934 regardless of theposition of the lift fans. Such an aircraft as described in the patent,is intended to take off in normal fashion using the conventional runwaysor, when required, it may lift vertically or with a short takeoff. Insuch an application the lift fans are able to produce about 60% of thevertical lift as horizontal thrust. This limitation is due to twofactors. One of these is the back pressuring on the fan as the exitlouvers are vectored rearward beyond about 40. The second is theperformance loss of the louver vanes themselves as they are required tooperate at high angles of attack.

As seen in the above patent, the fan exit louvers presently used forthrust vectoring are placed close to the fan stators. These exit louversare generally straight parallel venetian-blind types of louvers thatpivot about their spam on axes located just below the fan stators. Thissatisfactorily closes the surface opening through which the fluid movesand is adequate for a limited range of vectoring. Beyond about 40 ofvectoring by the louvers from the vertical, the pressure drop producedis objectionable. This occurs because as they are turned rearward thelouvers close down and reduce the exit area. The reduction of effectiveexit area throttles the fan significantly and the total force producedby the fan is reduced.

If the entire cascade of louvers were swung down from one end and thenmade longer, it can be seen that the effective area could be maintainedthe same and greater horizontal thrust vectoring could be obtained. Inother words, a greater flow area would be available. Of course, thedisadvantages of this arrangement are the mechanical complexities andthe lowering of such a large device as well as the means to turn theindividual louvers. An additional disadvantage is the leakage out of theside from the fan stream.

The present invention is directed to obtaining the same increasedvectoring effect without the need for dropping the cascade structure.All the advantages of a dropped cascade are obtained without thedisadvantage of me- 3,369,773 Patented Feb. 20, 1968 chanical complexityand the necessity for an additional duct to contain the flow through thecascades and prevent spillage out the sides.

The main object of the present invention is to provide 'a vane louversystem which minimizes, if not eliminates, the decrease in exhaust areawhen the individual louvers are actuated over a large operable range anddoes this by employing swept vanes.

Another object is to provide a vane louver system which may takenumerous forms of swept vanes to provide an area increase by addingperimeter to the vane system.

A further object is to provide such a vane louver system which avoidsthe loss normally inherent in conventional systems by presence of acenterbody because the invented system makes use of the centerbody areato add to the additional area obtained by the swept feature.

Briefly stated, the invention is directed to a swept vane louver system,such as a thrust vectoring system, which includes an opening throughwhich fluid may pass. A cascade of airfoils is provided over the openingand each airfoil is symmetrically swept back from an apex atsubstantially the midspan thereof. Hinge means are provided to connecteach airfoil at its ends in the opening to position the airfoils in flatclosing position over the opening. Means are provided to rotate theairfoils away from the surface in which the opening is located tominimize the decrease in discharge area when the airfoils are rotatedwith their apexes pointing downstream to vector the fluid from theopening. Various modifications are provided wherein each airfoil may be:moved a different angular amount from its adjacent airfoil and whereinthe span and chord as well as the sweep angle of each airfoil may differfrom its adjacent airfoil. Additionally, to correct angle of attackproblems, the camber of each airfoil may be varied on symmetricalportions adjacent the midspan.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed the invention will be better understood fromthe following description taken in connection with the accompanyingdrawings, in which:

FIGURE 1 is a partial view of a swept vane louver system as used in alift fan installation;

FIGURE 2 -is a partial cross-sectional view on line 2-2 of FIGURE 1 withthe louvers opened and showing the lift fan in phantom;

FIGURE 3 is a diagrammatic partial perspective view illustrating thearea increase obtainable;-

FIGURE 4 is a view similar to FIGURE 1 showing a modification of theswept vane louver system;

FIGURE 5 is a partial sectional view taken on line 5-5 of FIGURE 4 withthe louvers opened; and FIGURE 6 is a partial plan view of a modifiedsystem employing variable camber louvers.

For convenience, the invention herein will be described as it might beused in connection with the exit louver system as used in the abovementioned Patent 3,176,934. It should be noted however that it is notconfined toa circular opening nor is it confined to CXitdOuVEIS-bllt mayequally be used in an inlet louver system. However, for ease ofdescription and illustration, -it will .be described conveniently inthis manner and is limited only by the scope of the appended claims.

Referring first to FIGURE 1, there is shown partially an aircraft 10having wings 12 extending therefrom as viewed from the bottom. This is aconvenient illustration although the structure to be described could bedisposed within the aircraft or fuselage 10. In order to obtain verticalor short takeoff-lift where normal takeoff in the conventional fashionis not possible, the aircraft may be supplied with lift fans 13. Theseare well known and swept 3 completely described in the aforementionedpatent. It is customary to vector the thrust from the gas generator orthe lift fans in the illustration to provide for some forward propulsionwhen transitioning into the horizontal mode. To this end, and to providelift, the fan may be provided in an opening 14 in the wing surface 12 orany other surface. The opening 14 is designed to pass a fluidtherethrough in the well known manner. Movement of the fluid may beeither by the conventional lift fan shown or by direct lift engines orby horizontal engines that are exhausted through a duct or any otherwell known fashion. Sufiice to say, that the moving fluid eventuallyreaches the surface opening 14 and passes through it to impart thrust.conventionally, it is customary to provide a Venetian-blind cascade ofairfoil louvers across the outlet of the opening and, by actuating thelouvers, change the direction of thrust of the fluid. With a gasgenerator disposed above the exit louvers, any throttling due to closingthe louvers tends to back pressure the gas generator and, as shown, itback pressures the fan and reduces the fan output. Loss of thrust is theresult. Thus, it is necessary that the component above the louver systemsee at least a minimum decrease in area if it is not to be adverselyaffected. It should be noted that this also applies wherein the louversmay be used as an inlet system and no throttling is to occur into thedevice which is intended to use the incoming fluid.

In order to minimize the decrease in exhaust area, the inventionproposes to use a swept vane louver system preferably of V-shape asgenerally indicated in FIGURE 1 employing a cascade of swept airfoilvanes 16 that are conveniently symmetrically swept about a centerline18. Each airfoil has its apex 20 disposed on the centerline as shown.For the case of an outlet thrust vectoring system, as seen in FIGURE 2,the apexes are moved away from the surface and directed downstream asshown by arrow 22 which represents the direction of the fluid flowthrough the outlet louver system.

The term swept vanes is a well known term and, for the purposesintended, may be defined as any vane in which the swept surface is onethat is not at right angles to the fluid flow direction. Thus, itencompasses a curved surface or a series of straight surfaces which aregenerally symmetrical about an axis as shown in FIGURE 1 with the apexbeing the rearward point.

The swept vanes 16 are disposed to lie flat and preferably inoverlapping engagement over the surface opening 14 to close the openingin the non-operative position.

In order to obtain vectoring the airfoil vanes of the cascade aremovable by any conventional means 26 so that each airfoil is moved orrotated away from the surface.

In FIGURE 1, this means that the individual airfoils are rotateddownwardly to assume a position as shown in FIGURE 2. It has been foundthat excellent turning effects at high efficiency are obtained byrotating the individual airfoils a different angular amount from theadjacent airfoils so that, as shown in FIGURE 2, the angle x from thevertical may increase toward the aft direction so that x y z. As theairfoils 16 are pivoted to a vectored thrust position, the exhaust areadecreases. However, since the area in the vertical thrust position isgreater than that for straight airfoils, the area reduction in thevectored position relative to the vertical position is less than thatfor the straight airfoils. Thus, the minimization of the exhaust areadecrease enables a greater thrust output from an equivalent sized fan.As the airfoils are rotated by means 26 away from the surface, it willbe apparent that triangular shaped areas are uncovered by rotation ofthe V-shaped airfoils 16 downwardly. This triangular area is shown at 28in FIGURE 3. Thus, with the swept airfoils 16 it will be apparent thatrotation out of the surface opening increases the area by the triangularperiphery between the airfoils as at 28 which greater area is uncoveredin place of the conventional area 29 between straight airfoils.

It will be seen that the opening 14 as shown in FIG- URE 1 isconveniently round in the conventional fashion. This is not necessaryand it may be any shape that is convenient for the installation, e.g.,rectangular where the vanes are disposed at the end of a rectangularduct as in the outlet in US. Patent 3,028,121 and similar installations.With the circular opening, it will be apparent that the span of eachairfoil is different from its adjacent airfoil. Thus, as shown in FIGURE1, airfoil 16 is hinged at 30 and 32 at each end thereof in the opening.The span distance from hinge 30 to hinge 32 in the first airfoil isdifferent from that in the second louver which is longer than itsadjacent airfoil.

Normally, centerbody 24 in the straight-vane system represents ablockage. An advantage of the swept vane louver system is that the areaoccupied by the centerbody 24 is no longer an obstruction when theairfoils are moved away from the surface into the vertical thrustposition. The fluid will flow smoothly around the centerbody and makeuse of the individual airfoils directly under the centerbody since theyare moved away from the centerbody. The area of the centerbody is thusadded to the flow exit. By maintaining different angles, the flow areadecrease of the front portion of the fan is minimized for thrustvectoring while the rear portion of the fan discharge is vectored to agreater extent. The net result is that the overall fan exhaust area isminimized. Additionally, the movement of the airfoils does not open anyside passages because of the hinged connections 30 and 32. In otherwords, the same effect is obtained by the use of the swept vane louversystem as would be obtained by swinging the whole cascade down butwithout the disadvantages of the mechanical complexities. Thedisadvantage of the spillage effects around the side of the droppedcascade is avoided since the individual airfoils are connected to thesides of the opening.

The embodiment just described minimizes the reduction in exit or exhaustarea for thrust vectoring. Certain modifications will permit the areadecrease to be greatly minimized if not eliminated. This is shown inFIGURE 4, where, in addition to the advantages obtained by the sweptvane louver system just described, it will be apparent that the sweepangle 34 as well as the airfoil chords may together or individuallyadditionally change from each airfoil to its adjacent airfoil. In thiscase the individual airfoil louvers 36 may be similarly mounted at theirends in the opening as described in connection with FIGURE 1 andoperated in the same manner with the variable angles and chord and thedifferent span length when applied to a circular opening as shown.

In the different sweep angle effect as shown in FIGURE 4, it will beapparent that some airfoils 36 may occur in the circular configurationwhereby the depth 39 as shown in FIGURE 5 would be short if the firstairfoil were, like the rest, in the dotted position. This defect isovercome by the use of a double hinged airfoil as shown at 42 in FIGURE5 whereby the depth 40 is increased. With the use of hinge 41, thisprovides extra depth or distance 40 for the air to traverse for turning.As shown in FIG- URE 5, the different sweep arrangement of theindividual louvers may result in a considerably different envelope 43 ofthe louvers when open. This arrangement minimizes the area decrease byminimizing the reduction in distance between adjacent louvers in thevectored thrust position.

In addition to outlet application, the invention is applicable toinlets. To illustrate, FIGURES 4 and 5 may be thought of as applying toan inlet using the swept louver system wherein the airflow is then shownby the dotted arrow 4-4. The airfoil edges would, of course, becompatible with direction of fluid flow. The operation is the same inthat each airfoil extends up into the flow and is able to efficientlyhandle the flow and turn it in to a subsequent downstreamsurface openingor inlet. In this case, the louvers may be mounted on the upper surfaceof a wing in the same application. This merely illustrates theversatility of the swept louver system.

In addition to a limited angle of vectoring in the conventional system,there is another limitation in the angle of attack of the enteringfluid. In other words, the vanes cannot be turned too far even with thepresent swept system as so far described, or they begin to stall becausethe angle of attack gets too high. This merely means that the airstrikes the leading edge of the airfoil louvers at too large an angle topermit it to follow the louver surface and separation occurs. Thisproblem may be conveniently handled in the present invention by the useof variable camber airfoils in combination with the swept arrangement.Such variable camber airfoils may be of any suitable construction suchas that shown in US. Patent 3,172,621. Of course, in an applicationwherein variable camber airfoils are employed, the swept arrangementgenerally precludes the variable feature extending the full length ofthe span of each airfoil. In such an arrangement, as shown in FIGURE 6,a center fixed portion 46 may be provided at the midspan and thevariable camber feature may be provided, as in the above patent, onportions 48 connected to the midspan and symmetrically arranged adjacentthe midspan. The specific details of the mechanism to vary the camberare not important herein and the small loss that may be encountered inthe open position due to the fixed portion 46 is more than offset by theadditional advantages obtained by the variable camber portions 48.

It will be apparent that the swept vane louver system provides for atleast a constant area and the use .of the normally lost centerbody areafor larger turning capabilities than possible in the normal straightvane louver systems. The use of variable sweep angles permits evenlarger or increased areas. The provision of the means to vary the anglesbetween adjacent louvers merely provides flexibility for higherefliciency. The length of the span of each louver airfoil is dependenton the opening which must be covered resulting in different spans forcircular or nonrectangular openings. While not confined to anyparticular swept vane louver system, the V-shape arrangement as shown inFIGURE 1 where the sweep angle, the chord length, and the camber of allthe louvers are constant is preferred for simplicity, efiiciency, andease of manufacture. However, the other modifications shown offer theadditional advantages noted.

While there have been described preferred forms of the invention,obvious equivalent variations are possible in light of the aboveteachings. It is therefore to be understood that within the scope of theappended claims, the invention may be practiced otherwise than asspecifically described, and the claims are intended to cover suchequivalent variations.

I claim:

1. A vane louver system spanning an annular opening through which afluid passes said louver system comprisa cascade of airfoils straddlingsaid opening and having pivotally mounted ends,

each airfoil of the cascade being arched across the the opening forproviding a flow path area across the full span of said opening when theairfoils are pivoted to a position permitting flow,

whereby the reduction in flow area when the airfoils are pivoted tovector the fluid flow is minimized.

2. Apparatus as described in claim 1 having means to vary the camber ofeach airfoil on symmetrical portions adjacent the midspan.

3. Apparatus as described in claim 1 wherein the airfoils are V-shapedwith the apex of the V being movable away from said surface.

4. A thrust vectoring system comprising,

an annular opening for the discharge of fluid therefrom to produce athrust,

a cascade of airfoils, straddling said opening and having pivotallymounted ends, each airfoil being arched across the opening for providinga flow path area across the full span of said opening when the airfoilsare pivoted to a position wherein flow from said opening is permitted,

whereby the reduction in flow area when the airfoils are pivoted tovector thrust is minimized,

5. Apparatus as described in claim 1 further comprismg:

means for rotating said airfoils,

each of said airfoils being rotatable a greater angular distance from avertical plane than the airfoil on one side thereof,

whereby the flow area through one side of said opening is increased toprovide a maximum fluid flow for a given degree of flow vectoring.

6. Apparatus as described in claim 1 wherein,

said airfoils are generally V-shaped with the apex of the V beingmovable away from said opening,

the chord of each airfoil being greater than the airfoil on one sidethereof and the sweep angles of the airfoils varying so that the vanesare pivotable into overlapping closure of said opening.

7. Apparatus as in claim 1 wherein,

said airfoils are shaped to provide overlapping closure of said openingwhen positioned generally parallel to said opening.

References Cited MILTON BUCHLER, Primary Examiner.

T. W. BUCKMAN, Assistant Examiner.

